What is the expression in exponential form and value of -10x-10

It's very important to use the symbol " ^ " here to denote exponentiation.

You probably meant "-10x^(-10), which would be "-10 times x to the minus tenth power."

If you want the value, you could do the following:

        -10                   1
= - = - 10^(-9).
   10^10                10^9